Mesopotamia is a Greek word meaning, "Land between the Rivers." The rivers in question were and are the Euphrates on the west, and on the east the Tigris. Ancient Mesopotamia is considered the cradle of civilization in the Western World. It was the first to practice intensive year-round agriculture; it produced the first writing system, invented the potter's wheel and then the vehicular- and mill wheels, created the first centralized governments, law codes and empires, as well as introducing social stratification, slavery and organized warfare, and it laid the foundation for the fields of astronomy and mathematics.
The land of Mesopotamia lies between the Euphrates and the Tigris rivers; corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey, and parts of southwestern Iran. The people of this land usually divided the land between the rivers into two major regions, north and south. The northern region, a relatively high and arid land though not desert, they called Akkad. The lower southern region, almost at sea level, was called Sumer. From time to time, records speak of an intermediate region called "Babylonia", around the city of Babylon, but whether this was a geographical or a political distinction is uncertain.
The Euphrates River has in many ways marked a significant boundary between west and east: the nations on the western bank have commonly looked to the Mediterranean, while those on the eastern shore look to the region itself. Peoples dwelling on the eastern shores of the Tigris River tended to turn toward India and Persia. Its headwaters are in the high country of Armenia, and the river cuts its way through the Taurus mountains of modern-day Turkey and Syria, before flowing across the plateau of Akkad, and down through the garden country of Summer. South and west of the river are the deserts of Arabia and Transjordan: unsuitable country in those days for farming, but good for herding flocks of sheep, goats and camels. The Tigris has its headwaters in the same mountain range, but its course flows against the foothills of the Zagros Mountains. Where the Euphrates marked the line between desert and fertile farmland, the Tigris marked the boundary in ancient times between civilization and wilderness. It was a land of spirits and devils, and barbarians who washed with sand or not at all. Not until the rise of the great Persian empire would the lands beyond the river be thought worth visiting, though traders on their way to and from the civilizations of India often passed through. Between the rivers was a land rich with fertile soil and mud, but which had few trees and fewer resources of stone or metal. Though the highlands received much rain, the central basin between the rivers received most of its water from the outflowing rivers. This made irrigation projects a necessity throughout the region. Differences in geological structure divide this region into an upper and lower district; and this twofold physical division is reflected, as we shall see, throughout its political history.
The northern part of the valley, the portion that comprised ancient Assyria, consists of undulating plains, broken in places by mountain ridges. This region nourished a hardy and warlike people, and became the seat of a great military empire. The southern part of the valley, the part known as Babylonia or Chaldea, is, like the Delta region of Egypt, an alluvial deposit. The making of new land by rivers has gone on steadily during historic times. The ruins of one of the ancient seaports of the country - Eridu - lie over a hundred miles inland from the present head of the Persian Gulf. In ancient times, the land was protected against the river floods, and watered in seasons of drought, by a stupendous system of dykes and canals, which at present, although ruined and sand-choked, cover the area.
The economic activity of the river valleys was much like that of the Nile valley in Egypt. The luxuriant growth of grain on these river flats evoked the wonderment of Greek travelers who visited the East. Herodotus was afraid to tell the whole truth for fear that his veracity would be doubted. It is not strange that tradition located paradise in Mesopotamia, that primeval garden where "out of the ground made the Lord God to grow every tree that is pleasant to the sight, and good for food." (Genesis 2:9) This favored plain in a remote period of antiquity became the seat of an agricultural, industrial, and commercial nation in which the arts of civilization enjoyed one their earliest periods of development.
"Ancient History/Mesopotamia/Geography" (Wikibook) http://en.wikibooks.org/wiki/Ancient_History/Mesopotamia/Geography